Field of the Invention
The present disclosure relates to an organic light emitting display enabling duty control for turning on and off pixels, and a driving method of the organic light emitting display.
Discussion of the Related Art
An active-matrix organic light emitting display includes Organic Light Emitting Diodes (OLEDs). It has an advantage of providing a fast response speed with high light-emitting efficiency and luminance, and a wide viewing angle. An OLED includes an organic compound layer formed between an anode and a cathode. The organic compound layer is made of a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). If a driving voltage is applied to the anode and the cathode, a hole passed through the HTL and an electrode passed through the ETL move to the EML to form an exciton. As a result, the EML generates a visible light.
An OLED display device may be driven in a duty driving method. In order to implement the duty driving method, an emission control signal (hereinafter, an “EM signal”) is applied to pixels. The EM signal is applied at an ON level or an OFF level. The ON level defines a time of turning on the pixels, and the OFF level defines a time of turning off the pixels. In the case of an n-type Metal Oxide Semiconductor Field Effect Transistor (MOSFET), the ON level is a high logic level, and the OFF level is a low logic level. A Pulse Width Modulation (PWM) duty ratio of an EM signal defines times of turning on and turning off the pixels.
To implement the duty driving method, the OLED display device comprises an EM driver capable of switching from ON level to OFF level or vice versa in the desired time. The EM driver may be driven in response to an output of a gate driver. However, since the output of the gate driver is synchronized with data to be written to pixels, it is not possible to control the EM signal to be in the OFF level for a desired amount of time independent of the data. In addition, because a conventional EM driver generates an output in a clock timing, it cannot generate an EM signal with a duty ratio of 50% or greater. Therefore, there is a need for an EM driver which is capable of implementing the duty driving method.